Two-dimensional analysis of turn-on characteristics in AlGaN/GaN high electron mobility transistors (HEMTs) is performed by considering a deep donor and a deep acceptor in a buffer layer. Effects of buffer traps on gate lag are studied. It is shown that relatively large gate lag arises due to buffer traps, and it is correlated to large source access resistance in AlGaN/GaN HEMTs. The dependences of buffer-related gate lag on the gate length and buffer-trap parameters such as a deep-acceptor density and a deep donor's energy level are also studied. It is shown that the gate lag becomes smaller for a longer gate length because electron injection into the buffer layer occurs at the drain edge of the gate and normalized trapping effects become smaller. It is also shown that the gate lag becomes more significant when the deep-acceptor density in the buffer layer becomes higher, because the trapping effects become larger. In addition, the gate-lag rate is shown to be not so dependent on the deep-donor's energy level. Effects of surface states on gate lag are also described briefly.
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